Deformable sleeve nut and a method of manufacturing

ABSTRACT

Disclosed is a method of manufacturing a deformable sleeve nut that includes selectively strain hardening only a first portion of a material blank while not strain hardening a second portion of the material blank, then, after strain hardening the first portion of the material blank, internally threading the first portion of the material blank to define a nut portion and machining the second portion of the material blank to define a deformable sleeve portion that includes an end portion and a bulbing portion positioned between the end portion and the nut portion, where the bulbing portion is constructed to bulb outwardly and form a load bearing flange when the bulbing portion is compressed between the end portion and the nut portion. Also disclosed is a deformable sleeve nut made with this process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims the benefitof U.S. application Ser. No. 14/881,237, filed on Oct. 13, 2015,entitled “A DEFORMABLE SLEEVE NUT AND A METHOD OF MANUFACTURING,” whichclaims the benefit of Provisional Patent Application No. 62/063,040filed Oct. 13, 2014, which is hereby incorporated by reference.

BACKGROUND

Blind fasteners and clamps are widely used. Applicant's OSI-Bolt®Fasteners is a type of blind fastener that is used in both composite andmetallic airframe application as both a primary and secondary fastener.(Primary fasteners are subjected to more severe joint loads thansecondary fasteners.) Blind type fasteners, where the blind sideclamping surface is inserted through the fastener opening beforeengaging the blind side clamping surface, are popular because, unliketwo-piece fastening systems that require where access to both sides ofthe fastener, the installation of a blind type fastener can often befacilitated from just one side of the fastener opening. This cansimplify installation, particular when robotic installation is used, andalso permits using blind fasteners in application where access to oneside of the opening is restricted or unavailable, for example, in aclosed structure such as some aircraft wings.

In situations where access to both sides of the blind fastener isrestricted, if a failure occurs on the blind side, it can be difficultand time consuming to remove the failed fastener and replace it with anew fastener. There is a need for improved blind fasteners that reliablyperform as expected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view, partially in section, of a prior artassembled OSI blind fastener including a bolt, a nut, a sleeve and abody.

FIG. 2 is a front elevational view of the prior art FIG. 1 sleeve.

FIG. 3 is a side elevational view, partially in section, of the priorart FIG. 2 sleeve.

FIG. 4 is a front elevational view of the prior art FIG. 1 nut.

FIG. 5 is a side elevational view, partially in section, of the priorart FIG. 4 nut.

FIG. 6 is a flow chart of a method of manufacturing a deformable sleevenut.

FIG. 7 is a front elevational view of a material blank.

FIG. 8 is a side elevational view of the FIG. 7 material blank.

FIG. 9 is a side elevational view of a material blank after partialstrain hardening.

FIG. 10 is a front elevational view of a deformable sleeve nut.

FIG. 11 is a side elevational cross-sectional view of the FIG. 10deformable sleeve nut taken along lines 11-11 in FIG. 10.

FIG. 12 is a side elevational view, partially in section, of a blindfastener which includes the FIG. 10 deformable sleeve nut.

FIG. 13 is a side elevational view, partially in section, of the FIG. 12blind fastener after it has been fastened to two panels.

FIG. 14 is a hardness chart showing the KNOOP hardness along the lengthof five partial strain hardened deformable sleeve nuts.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of whatis claimed, reference will now be made to embodiments illustrated in thedrawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theclaims is thereby intended. Any alterations and further modifications inthe illustrated device, and any further applications of the principlesdisclosed and illustrated herein are contemplated as would normallyoccur to one skilled in the art to which the disclosure relates.

Referring to FIG. 1, a prior art OSI fastener is illustrated as fastener50. Fastener 50 includes bolt 60, body 70, nut 80 and sleeve 90. Sleeve90 is also illustrated in FIGS. 2 and 3 and nut 80 is also illustratedin FIGS. 4 and 5. After inserting fastener 50 into an opening andsecuring body 70 from rotating, rotation of bolt 60 relative to body 70compresses sleeve 90 between body 70 and nut 80 causing sleeve 90 tobulb outwardly generating an enlarged flange that forms an enlargedclamping surface that cannot pass through the opening. Continuedrotation of bolt 60 relative to body 70 moves the enlarged flange intocontact with the part(s) being claimed and applies a clamping forcebetween the enlarged flange from sleeve 90 and head 72 on body 70.

Fastener 50 requires a non-rotating interface between body 70, sleeve 90and nut 80 because only body 70 can be secured from rotation duringinstallation (nut 80 and sleeve 90 are inserted through the fastenerhole and are not accessible in a “blind” installation). Thus, securingbody 70 from rotating should also secure nut 80 from rotating, otherwisenut 80 could rotate with bolt 60 rather than compressing and advancingsleeve 90 to complete installing the fastener due to threaded engagementwith bolt 60. To enhance a non-rotating interface, the end of body 70that contacts sleeve 90, both ends of sleeve 90 and the end of nut 80that contacts sleeve 90 may be knurled or otherwise include featuresthat interlock sleeve 90, nut 80 and body 70 to reduce or preventrelative rotation between these components during installation. This isshown as knurling 82 on nut 80 in FIGS. 4 and 5 and knurling 92 onsleeve 90 as shown in FIGS. 2 and 3.

Fastener 50 utilized separate sleeve 90 and nut 80 structures becausethese components generally require different material characteristics.Sleeve 90 generally requires significant ductility to permit theformation of an enlarged flange while nut 80 generally requiressignificant strength to prevent internal threads from being stripped bybolt 60 and be sufficiently hard such that nut 80 does not significantlydeform when a load is applied while, at the same time, sleeve 90 doesdeform. With separate components, material selection for sleeve 90 andnut 80 can be separately optimized for a particular application. Aductile material can be selected for sleeve 90 while a stronger, heattreated (hardened) material can be used for nut 80. For example,Applicant uses a material such as titanium or steel that has beenhardened by heat treating to construct nut 80 while a malleablematerial, such as a solution treated AISI 304 Stainless Steel, is usedfor sleeve 90.

Applicant has identified that the two piece construction for nut 80 andsleeve 90, while addressing the required physical characteristics forthese components, may cause other problems. Slippage between nut 80 andsleeve 90 results in a failed installation, because there is noalternative mechanism to hold nut 80 against rotation of bolt 60. Thiscan be a significant problem if slippage occurs after partial expansionof sleeve 90, so that fastener 50 cannot be easily removed butinstallation cannot be completed without scrapping fastener 50, whichmay require cutting fastener 50 off. There is a need for an improved nutand sleeve combination that reduces the occurrence of failedinstallations.

Applicant has identified that by combining the nut and sleeve structureinto a single structure, failure modes that previously occurred at thejunction between the nut and sleeve structures can be significantlyreduced or eliminated. However, the problem of different materialperformance requirements for these structures remains. Applicantssolution to this problem is to selectively strain harden the portion ofa material blank that is used for the nut portion while not strainhardening the remaining portion of the material blank that is utilizedto form the deformable sleeve portion of the combined structure.

Referring to FIG. 6, process 100 is illustrated. Process 100 is amanufacturing process to produce a deformable sleeve nut that combinesfunctions similar to nut 80 and sleeve 90 in a unitary structureconstructed from a single piece of material. Process 100 begins withstep 102 where a first portion of a material blank is selectively strainhardened while a second portion of the material blank is not strainhardened. Strain hardening process such as extruding and roll formingcan be used in step 102. Process 100 continues with step 104 where thefirst portion of the material blank is machined and internally threadedto define a nut portion of the deformable sleeve nut. In step 106, thesecond portion of the material blank is machined to define a deformablesleeve portion. In step 108, a transition between the nut portion andthe deformable sleeve portion is machined. The transition can be conicalin shape or any other desired geometry. In step 110, the outer surfaceof the material blank, including the nut portion and the deformablesleeve portion, is machined to have a constant outer diameter.

It should be understood that steps 104, 106. 108 and/or 110 in process100 may be performed in any desired sequence and/or at the same time.For example, the material blank may require a boring operation thatpasses through both the first and second portions as part of forming thenut portion and the deformable sleeve portion. Similarly, the outsidesurface could be formed before internal features are formed.

Referring to FIGS. 7 and 8, material blank 120 is illustrated. Materialblank 120 has a length L1 and an outer diameter OD1. Material blank 120is a continuous piece of a single material such as AISI 304 StainlessSteel. Other materials that are acceptable to use as material blank 120include 300 and 400 series stainless steels and A 286 PrecipitationHardening Alloy.

Referring to FIG. 9, partially cold worked material blank 130 isillustrated. Partially cold worked material blank 130 includes coldworked portion 132, un-worked portion 136 and head 138 with transition134 located between cold worked portion 132 and un-worked portion 136.Cold worked portion 132 is formed by a trapped extrusion processperformed on a solution treated material blank 120. Transition 134 maybe partially cold worked, but is less cold worked than cold workedportion 132. Head 138 is formed by cold working after cold workedportion 132 is formed. Head 138 is primarily formed to aid in orientingand handling cold work blank 130 during subsequent steps such asmachining.

Referring to FIGS. 10 and 11, deformable sleeve nut 140 is illustrated.Deformable sleeve nut 140 includes nut portion 142, transition portion144 and deformable sleeve portion 146. Deformable sleeve nut 140 has anouter surface 147 that has a diameter OD3. Deformable sleeve nut 140 mayhave a constant diameter OD3 across substantially its entire length. Nutportion 142 is internally threaded with internal threads 148 definingmajor diameter 150. In the illustrated embodiment, transition portion144 includes conical taper 152 that has a vertex angle VA, although theconical transition geometry is not limiting. In the illustratedembodiment, vertex angle VA is approximately equal to 15 degrees. Inother embodiments, vertex angle VA can vary from between 10 degrees and25 degrees. In yet other embodiments, vertex angle VA can vary frombetween 5 degrees and 90 degrees.

Deformable sleeve portion 146 also defines and includes internaldiameter 154, insert recess 156 and end wall 158. In the illustratedembodiment, internal diameter 154 is approximately equal to majordiameter 150. Insert recess 156 may be constructed and arranged toreceive a plastic insert that may assist deformable sleeve portion 146to preferentially bulb outwardly while potentially blocking deformablesleeve portion 146 from buckling inwardly upon application of acompressive force. While not illustrated, end wall 158 may optionallyinclude geometries such as knurling to reduce or eliminate rotationagainst a body such as body 70.

Referring now to FIG. 12, fastener 200 is illustrated. Fastener 200includes deformable sleeve nut 140, bolt 160, body 170 and insert 180.Bolt 160 includes external threads 162, head 164 and engaging portion166 that is constructed and arranged to interface with an external toolto rotate bolt 160. Bolt 160 also optionally includes break groove 168positioned between engaging portion 166 and head 164. Break groove 168may be constructed and arranged to fracture when sufficient torque isapplied to engaging portion 166, such as may be encountered whenfastener 150 is fully installed as described below.

Body 170 defines bore 172 through which bolt 160 passes. Body 170 alsoincludes tapered end 174 and head 176, which head 176 defining engagingportion 177 and surface 178. Engaging portion 177 is constructed andarranged to interface with an external tool to secure the relativeposition of body 170 when bolt 160 is rotated. Tapered end 174 mayoptionally include anti-rotation features such as knurling, which isshown in FIG. 12.

Insert 180 is positioned in insert recess 156. Insert 180 may define asubstantially cylindrical shape. Insert 180 may be constructed from arelatively easily deformable material (compared to deformable portion146) such as plastic. Insert 180 may be constructed and arranged tosubstantially fill the space between bolt 160 and deformable sleeve nut140 defined by insert recess 156. Insert 180 may have sufficientcompression strength to encourage deformable portion 146 to bulboutwardly when compressed while potentially blocking deformable sleeveportion 146 from buckling inwardly upon application of a compressiveforce.

Fastener 200 is assembled with bolt 160 passing through bore 172 in body170, with threads 148 on deformable sleeve nut 140 threadingly engagedwith threads 162 on bolt 160 with end 158 of deformable sleeve nut 140abutting tapered end 174 of body 170.

Fastener 200 is installed by inserting it into an appropriate sizedopening, securing body 170 and deformable sleeve nut 140 from rotatingby securing engaging portion 177 with an appropriate tool and thenrotating bolt 160 relative to body 170 utilizing a tool engaged withengaging portion 166 to cause deformable sleeve nut 140 to advance alongbolt 160 toward body 170, thereby compressing deformable sleeve portion146 between nut portion 142 and tapered end 174 on body 170. This causesdeformable sleeve portion 146 to bulb outwardly and fold upon itself toform an enlarged flange.

Referring now to FIG. 13, fastener 200 is shown as installed throughoverlapping plates 201 and 202 as installed fastener 200′. Installeddeformable sleeve nut 140′ has been advanced toward body 170sufficiently that deformed sleeve portion 146′ has bulbed outwardly andadvanced up tapered end 174, thereby expanding the internal diameter ofdeformed sleeve portion 146′. Deformed insert 180′ is positioned insidebulbed flange 190 formed by deformed sleeve portion 146′. Overlappingplates 201 are clamped together between bulbed flange 190 and surface178 on head 176.

Referring to FIG. 14, a chart of the hardness distribution along thelength of deformable sleeve nut 140 is illustrated. The X-axis of thechart shows the relative position, measured in inches, long the lengthof deformable sleeve nut 140 where hardness was tested. The Y-axis ofthe chart shows the measured Knoop hardness, measured with a 500 g load.The chart includes the results of 5 different specimens, each made ofAISI 304 Stainless Steel, each having been subject to partial 33% coldworking. Samples 1 through 3 were manufactured from one heat of rawmaterial. Samples 4 and 5 were manufactured from a different heat of rawmaterial. The location “0” starts at the threaded end of deformablesleeve nut 140, with larger measurement progressively advancing alongthe length of deformable sleeve nut 140 toward deformable sleeve portion146.

As illustrated in FIG. 14, the method of partially cold working thematerial blank resulted in selectively hardening the portion of theblank cold worked. With nut portion 142 averaging approximately twicethe hardness of deformable sleeve portion 146, with a distincttransition in the hardness at transition portion 144.

Additional testing also revealed that the ratio between the maximum andminimum measured hardness varies based on the size of the deformablesleeve nut produced (smaller deformable sleeve nuts are manufacturedusing smaller material blanks). Testing on ¼ inch diameter deformablesleeve nuts subjected to partial 33% cold work measured hardness ratios(max/min) of 1.85, 1.91, 1.92 and 1.87. Conversely, testing on 3/16″diameter deformable sleeve nuts subjected to partial 33% cold workmeasured hardness ratios (max/min) 2.31, 2.53, 2.79. In subsequentinstallation testing on the 3/16″ diameter deformable sleeve nuts, thecorebolt occasionally fractured during the installation process,indicating that the amount of cold work might need to be reduced for the3/16″ parts compared to the ¼″ parts. Based on this data, nut portion142 should be at least seventy-five percent harder than the hardness ofdeformable sleeve portion 146 but no more than one hundred and fiftypercent harder.

Table 1, below, reports additional measured hardness ratios for ¼″sleeves and 3/16″ sleeves subjected to partial 33% cold work.

TABLE 1 Hardness Ratios Sleeve-Nut Raw Material Cold Work Reduction/Hardness Size Lot # Equipment/Method Ratio 08 (¼″ OD) 20361 33% Header1.67 Trapped Extrusion 1.49 1.57 1.78 1.81 1.79 004205A 33% TensileTester 2.08 Trapped Extrusion 2.15 2.13 06 ( 3/16″ OD) 16887 33% TensileTester 2.12 19435 Trapped Extrusion 1.77 19435 2.55 16887 2.40 194352.40

All the specimens listed in Table 1 where determined to have beenadequately work hardened, but, as already discussed, some of the 06parts ( 3/16″ OD) might require less hardening. The difference betweenthe equipment used, i.e., tensile tester vs. header, is the speed of theextrusion process. The header is much quicker at cold working the parts,around 60 pieces a minute, while the tensile tester (in an R&D lab) tookaround 15-20 seconds to extrude a single blank. There were alsodifferences in the material lots tested. Lot #20361 was wire in solutiontreated condition while the rest of the lot numbers were bar stock whichwas machined to the correct size before solution treating the blanks.(All specimens were solution treated before cold working.)

While the claimed subject matter has been illustrated and described indetail in the drawings and foregoing description, the same is to beconsidered as illustrative and not restrictive in character. All changesand modifications that come within the spirit of the disclosure aredesired to be protected by the claims.

1. A method of manufacturing a single-piece fastener nut and sleevestructure, the method comprising: providing a selectively hardenedmaterial blank having a nut portion having greater hardness thanremaining portions of the material blank; boring the material blank andinternally threading the nut portion; and machining a sleeve portionwithin a section of the remaining portions of the material blank,wherein the machining forms: (i) a bulbing portion positioned between aterminal end of the material blank and the nut portion, and (ii) aconical transition portion, positioned proximate to the bulbing portion,and having a vertex angle of between 10 and 25 degrees; and wherein thebulbing portion is constructed and arranged to bulb outwardly and form aload bearing flange when the bulbing portion is compressed between theend portion and the nut portion. 2-3. (canceled)
 4. The method of claim1, wherein the conical transition portion defines a vertex angle ofapproximately equal to 15 degrees.
 5. The method of claim 1, wherein thesleeve portion defines an internal diameter approximately equal to amajor diameter of the internal threads in the nut portion.
 6. The methodof claim 1, wherein the nut portion of the material blank is strainhardened using a strain hardening process selected from the groupconsisting of: extruding and roll forming.
 7. The method of claim 6,wherein strain hardening the nut portion of the material blank reducesthe cross-sectional area of the first portion of the material blank atleast 30%.
 8. The method of claim 6, wherein, after strain hardening,the hardness of the nut portion is at least seventy-five percent harderthan the hardness of the second portion.
 9. The method of claim 1,further comprising machining an outside surface of the material blank tohave a substantially constant outer diameter across the nut portion andthe deformable sleeve portion. 10-20. (canceled)
 21. The method of claim1 wherein the nut portion has up to twice the hardness of the sleeveportion that is formed from the remaining portions.
 22. The method ofclaim 1 wherein the material blank consists of A 286 PrecipitationHardening Alloy.
 23. The method of claim 1 wherein the nut portion isformed by a trapped extrusion process performed on a solution treatedmaterial blank.
 24. The method of claim 1 wherein the selectivelyhardened material blank includes a transition portion having a hardnessthat is less than the nut portion but greater than the remainingportions.
 25. The method of claim 1 wherein the selectively hardenedmaterial blank comprises heat-treated titanium.